Mouse adrenal tumor cells in monolayer tissue culture respond to picogram quantities of cholera enterotoxin by undergoing morphologic changes and increasing their production of delta 4,3 ketosteroids. With the aid of a mutant adrenal cell line, differences between the mechanisms of action of cholera enterotoxin and the natural hormonal inducer, ACTH, can be demonstrated. What we propose to do during the coming year is to define some of the molecular changes taking place in cells being stimulated by the toxin and to see how these changes compare to those effected by ACTH. Specifically, rates of protein, RNA and DNA syntheses will be examined, as will be changes in the intracellular contents of cyclic AMP. The cells will also be examined for permeability changes secondary to toxin or ACTH exposure. The effects of inhibitors of protein, RNA and DNA syntheses on the toxin's steroidogenic effects will also be assessed. Finally, direct investigations on the nature of the cellular receptor sites for cholera enterotoxin will be started, using radiolabelled toxin.